PALM HARBOR, Fla. — Padraig Harrington knew he was playing better golf than his scores indicated. He just wasn’t expecting the lowest official score of his life, a 10-under 61 to set the course record Thursday in the Transitions Championship.

Harrington took a step toward ending 17 months and 37 tournaments without a victory when he made 10 birdies, including a 75-footer late in his round, to build a three-shot lead among the early starters at Innisbrook.

“I play better on the Monday, Tuesday, Wednesday than I do on the Thursday, Friday, Saturday, Sunday,” Harrington said. “I’m trying to stay patient. I know my game is good. One of the hardest things is to wait with confidence. I’m feeling like things are ready to happen. Obviously, today it showed the potential. Today is a peak. But we’ll wait and see what happens over the next number of weeks.”

With a 15-foot birdie putt on the 18th — how could it not go in the way his day was going? — he broke by one shot the record at the esteemed Copperhead Course at Innisbrook that had been held by Mark Calcavecchia in 2007 and Jeff Sluman in 2004.

Harrington’s previous best was a 62 three times, most recently at the 2009 Portugal Masters. He also had a 61 at the Nedbank Challenge in 2001, an unofficial event. It was not recognized as a course record because of preferred lies.

Not only was Harrington three shots better than anyone else, it was nearly 8.7 shots better than the course average.

Will Claxton birdied the 18th for a 64, a score that would have put him atop the leaderboard at Innisbrook the last seven years. John Senden, coming off a 65 in the final round at Doral, was in a large group at 66 that included William McGirt and 51-year-old Kenny Perry, making a rare appearance on the PGA Tour.

Doral winner Justin Rose and Luke Donald were at 67, while defending champion Gary Woodland opened with a 68.

Did anyone see a 61 at Innisbrook?

“I did. I watched it,” said Geoff Ogilvy, who played alongside Harrington. “On the first tee, I didn’t see 61. But after you see it done ... the only really, completely unreasonable birdie was on the 17th. There was never any stress.”

That birdie putt on the 17th was from 75 feet, and Harrington said it looked good for the last 15 feet.

But if there was one putt that reminded him how everything was falling his way, it was the 6-foot birdie on the 16th, atop a crown in such a way that Harrington wasn’t sure which way it was going to break. He guessed right.

“You’re really guessing at which way it’s going to go, but on your day, it goes the right way,” he said. “I guarantee you there will be a lot of players having a frustrating day, telling you they hit it exactly where they wanted and it missed.”

With a wedge into 15 feet on the last hole, he had no doubt.

“When it’s your day, I could have turned my back on the hole and I would have holed the putt on the last,” Harrington said. “That’s just the way it is when things are going for you.”

Not much has been going well for the three-time major champion since he last won the Johor Open in October 2010. Though he tinkers endlessly with his swing, Harrington had trouble scoring.

He has been working with Pete Cowen, and in January began seeing Dave Alred, whom he refers to as a practice coach. Alred also works with Luke Donald as the Englishman rose to No. 1 in the world, though he is best known in rugby circles as a kicking coach for the likes of Jonny Wilkinson.

Harrington said it’s all about practicing with a purpose, which he has done. He can’t work much harder. The toughest part of this has been waiting for it all to come together, which is exactly what happened on a gorgeous day near the Gulf coast of Florida, with only a mild breeze and minimal rough.

The longest putt for par he had all day was about 4 feet on the third hole. Harrington hit so many quality shots that he allowed the thought of a 59 to creep into his head. He was 6 under through 10 holes and had an easy, uphill birdie putt from 6 feet on the par-5 11th.

“I got over it and started thinking, `If I hole this, I’m 7-under par, seven holes to go, I only need to make five more birdies,”’ he said. “I just got totally out of where I should have been, hit a bad putt and missed. But if anything, it kind of got the 59 out of my head. So as much as I did choke, it made it easier for the rest of the holes.”

Harrington said he never shot lower than 60 as an amateur, back when he went at every flag, before he accrued what he called “fear and damage in my system.” He did have a 61 at the Nedbank Challenge a decade ago, though it didn’t count as a course record because it was preferred lies that day.

Stewart Cink and David Toms were among those at 67, while Sergio Garcia had a 68.

Innisbrook wasn’t easy for everyone. Masters champion Charl Schwartzel opened with a 76, while Matt Kuchar had a 73.

Harrington, who rose to No. 3 in the world three years ago, has fallen to No. 90. He remains eligible for the majors, though the reality of how far he has dropped was evident over the past month. He missed the Match Play Championship for the first time since 1999, and he was not eligible for the World Golf Championship at Doral.

“It’s not a wake-up call because it’s not like I could be working any harder, or trying any harder,” he said. “You feel like you’re good enough. But if your performances are not good enough, you have no else to blame. It is a little frustrating. But I’m working, like everybody else — working to keep a good attitude and be patient and let it happen and look at the positives.”

That’s never been a problem. Even during this slump, Harrington rarely lets a pro-am round go by when he doesn’t invite his amateur partners to lunch. He endorses the Special Olympics, and took time Wednesday to meet with one of the athletes, whom he described as being “just happy with life, and it’s infectious.”

Asked about the low point during this slump, Harrington shook his head.

“I’m a professional golfer,” he said. “There isn’t a low point in being a professional golfer. I mean, let’s be realistic.”